JPH0981967A - Optical recording medium and recording and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease crosstalks from adjacent tracks even if signals are recorded in both of land and groove by limiting the groove depth. SOLUTION: This optical recording medium is constituted by successively laminating a dielectric layer, phase change type recording layer, dielectric layer and metallic reflection layer on a transparent substrate 1 on which grooves 4 are formed. The recording, erasing and reproducing of information are executed in the optical recording medium by using both of the regions on the grooves 4 and on the lands 3 as recording regions and irradiating the recording medium with a laser beam of a wavelength of <=700nm. The recording medium satisfies equation II, equation III (where m: integer) when the groove width is 0.3 to 0.8μm, the land width is 0.3 to 0.8μm and the groove depth (d) is equation I (where, λ: the wavelength of irradiation light, n: the refractive index of the substrate 1, d: the depth of the grooves) and when the larger of the reflectivity is defined as Rhigh%, the lower as Rlow% and the phase difference Q of the reflected light from the unrecorded regions and the recorded regions as equation IV. Further, the optical recording medium is so constituted that the land width LW satisfies equation V (where, NA: the numerical aperture of a focusing leans) and the groove width GW and land width LD satisfy equation VI.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium and a recording / reproducing method, and an optical information recording for recording, reproducing and erasing information on both the groove portion and the groove portion of a substrate by irradiating a laser beam. The present invention relates to a medium and a recording / reproducing method.

[0002]

2. Description of the Related Art In recent years, a recording medium capable of recording and reproducing a large amount of data at high density and at high speed has been demanded as the amount of information has increased. Optical discs are expected to meet such applications. There is. The demand for higher capacity and higher density in such a recording medium is inevitable in the era when the recording medium and the recording device were imposed in handling a huge amount of image information and audio signals, and digital modulation technology and data compression technology. Keeping pace with the progress of, the progress is just progressing.

As a specific means for increasing the density, in the optical disc, the wavelength of the light source is shortened and the NA of the lens is increased.
MCAV which reduces the convergent beam diameter of the irradiation light by shortening the recording mark length by shortening the recording mark length by increasing the optical aperture, and increases the recording frequency toward the outer circumference under a constant rotation speed to keep the recording density at the inner and outer circumferences constant. ModifiedCo
nstant Angular Velocity),
Mark edge recording, which puts information on the start and end of the mark, has been developed and used, and in the present situation, a method for further increasing the density is being sought.

In a recordable optical disk, a guide groove is previously formed on the disk to form a so-called track. Normally, information signals are recorded and collected by condensing laser light between or within the guide grooves.
Playback or deletion is performed. In general optical disks currently on the market, information signals are usually recorded only between the guide grooves or inside the guide grooves, and the other is a boundary for separating adjacent tracks to prevent signal leakage. It just plays a role.

[0005] If it is possible to record information in this boundary portion, for example, in the guide groove when recording between the guide grooves, and between the guide grooves when recording in the guide groove, if it is possible to similarly record information. The recording density is doubled, and a large improvement in the recording capacity can be expected. Hereinafter, a method of recording information on both the groove and the guide groove, the land between the guide grooves, and both the land portion and the groove portion will be described as L & G recording.

As a proposal for L & G recording, Japanese Patent Publication No. 63-5
7859, etc., but when such a technique is used, it is necessary to pay great attention to the reduction of crosstalk. That is, in the L & G recording described in Japanese Patent Publication No. 63-57859, since the distance between the recording mark train of a certain track and the recording mark train of the adjacent track is half the convergent beam diameter, the recording mark train to be reproduced is The convergent beam diameters overlap to the adjacent recording mark row.

For this reason, there is a problem that the crosstalk during reproduction is increased and the reproduction S / N is deteriorated. In order to reduce this crosstalk, for example, SPIE Vo
l. 1316 Optical Data Storage
e (1990) pp. 35, there is a method for reducing crosstalk by providing a special optical system and a crosstalk cancel circuit in the optical disc reproducing apparatus.

However, this method has a demerit that the optical system and the signal processing system of the apparatus become more complicated. As a method for reducing crosstalk without providing a special optical system or signal processing circuit for reducing playback crosstalk, equalize the width of the groove (guide groove) and the land (between guide grooves). There is a proposal that it is effective to set the groove depth within a certain range corresponding to the reproduction light wavelength. (Jpn. J. Appl. Phy
s. Vol32 (1993) pp. 5324-532
8).

According to this, the crosstalk is reduced when the land width = the groove width and the groove depth is λ / 7n to λ / 5n (λ: reproducing light wavelength, n: refractive index of the substrate). Are shown as calculated and experimental facts. This is also described in JP-A-5-282705.
According to the CN ratio (carrier / noise ratio) and the groove depth dependency of crosstalk described in this paper, the effect of reducing crosstalk can be seen by optimizing the groove depth. And the CN ratio in the groove is unbalanced.

When L & G recording is performed, a difference occurs between the carrier level of the land portion and the carrier level of the groove portion, and as a result, the CN ratio on one side is significantly reduced.
It is not desirable in the signal quality of the disc. On the other hand, when the track pitch is reduced due to the high density, normally, the track pitch and the groove shape may be selected so that the amount of crosstalk is below a predetermined level. , There is another issue to consider.

There is a problem that when a certain track is repeatedly overwritten, the amorphous bits on the adjacent tracks disappear (recrystallize). The reason for this is not clear, but the adjacent track is heated by the weak laser light in the skirt portion of the intensity distribution of the focused light beam during recording on the adjacent track, and the temperature of the amorphous bit portion becomes higher than the crystallization temperature. It is thought that this is because it is heated.

[0012] The time is several hundred nanoseconds per time, but is gradually recrystallized during repeated heating. For example, when the overwrite is repeated 10,000 times, the C / N ratio (carrier-to-noise ratio) of the adjacent track, which is 55 dB at the initial stage, may be reduced to less than 50 dB.

This problem is hereinafter referred to as cross erase. In a phase change medium, it is more than optical diffraction limit.
We must keep in mind the minimum track pitch due to cross erase, but the limit was not always clear. Furthermore, as a result of our earnest study, when the groove width was narrowed while keeping the groove and land widths at 1: 1 to increase the density by narrowing the track pitch, the previous mark after repeated overwriting It has been revealed that the characteristics of the land portion are significantly deteriorated in terms of the remaining marks and the deterioration of the recording mark jitter.

[0014]

SUMMARY OF THE INVENTION The present invention is to solve the above problems, and particularly in an L & G recording type optical disc using a laser light having a wavelength of 700 nm or less as a light source, the carrier level of the recording mark of the land portion and the groove portion. It is an object of the present invention to eliminate the above-mentioned imbalance and to provide a high density optical disc that can obtain the same high signal quality regardless of whether recording is performed on the land portion or the groove portion.

[0015]

The present invention has been made as a result of repeated studies on the regulation of the groove depth and the phase difference of the reflected light from the unrecorded area and the recording mark. A dielectric layer, a phase-change recording layer, a dielectric layer, and a metal reflection layer are sequentially laminated on the formed transparent substrate, and both the groove and the land are used as a recording region, and a wavelength of 700 nm or less is used. An optical recording medium that records, erases, and reproduces information by irradiating the laser beam of (1), having a groove width of 0.3 μm to 0.8 μm and a land width of 0.3 μm to 0.8 μm. And the groove depth d satisfies the following inequality:

[0016]

[Formula 7] λ / 7n <d <λ / 5n (λ: wavelength of irradiation light, n: refractive index of substrate, d: depth of groove)

(2) Of the reflected light from the unrecorded area and the reflected light from the recorded area defined below, the one with the higher reflectance is R _high (%), and the one with the lower reflectance is R _low (%), Assuming that the phase difference between the reflected light from the unrecorded area and the recorded area is α, the following equation is satisfied,

[0018]

(8) 10 ≦ R _high ≦ 40

[0019]

## EQU9 ## R _low / R _high ≦ 0.15 mπ ≠ α (m is an integer) where α = (phase of reflected light from unrecorded area) − (phase of reflected light from recording area)

(3) The land width LW satisfies the following equation,

[0021]

0.62λ / NA < LW < 0.8λ / NA where λ is the wavelength of the irradiation light and NA is the numerical aperture of the focusing lens.

(4) The groove width GW and the land width LW satisfy the following equation.

[0023]

[Equation 11] (LW + GW) / 2> 0.6λ / NA

An optical recording medium characterized by the above. With the configuration described above, in the optical disc of the present invention, the signal quality (carrier level) of the recording mark is the same regardless of whether recording is performed on the land portion or the groove portion. Further, the present invention relates to an optical information recording medium characterized in that the pitch of recording tracks is larger than 0.6λ / NA (λ: light beam wavelength, NA: numerical aperture of focusing lens).

Further, in order to guarantee durability against repeated overwriting in the land portion, the land width (hence, the groove width is substantially equal) is set to 0.62λ / NA or more and 0.8λ / NA or less. And an optical information recording medium. These are indispensable provisions for ensuring the reliability of the optical disc of the L & G recording system in which a laser beam having a wavelength of 700 nm or less is used as a light source. How the present invention works and effects in the reproducing process of the optical recording medium for land & groove recording will be explained in detail below by using a simple model as to the basis of its effectiveness.

FIGS. 1 to 4 are schematic views showing the case where the reproducing light beam is irradiated onto the land or groove of the L & G optical disk. Layers other than the recording layer 2 are omitted for easy viewing of the drawing. The reproduction light beam is condensed using an objective lens or the like, and is assumed to be irradiated onto the disc from the substrate 1 side, and is hereinafter referred to as a converged beam. 1 and 3 show the case where the convergent beam 5 exists in the unrecorded area, and FIGS. 2 and 4 show the case where the convergent beam 6 exists on the recording mark 8.

The assumption is that the recording mark 8 is sufficiently longer than the convergent beam 5 to simplify the calculation. As will be shown later in Examples, there is no problem even if the recording mark is actually shorter than the convergent beam diameter. Here, the state of the recording layer when not recorded is defined as a crystalline state, and the state of the recording layer when recorded is defined as an amorphous state.

The intensity of the convergent beam has a Gaussian distribution according to an actual model, and the beam diameter is defined as 1 / e ² of the central intensity. Assuming that the width of the land 3 (land width) and the width of the groove 4 (groove width) are equal and half the beam diameter, the step between the land 3 and the groove 4 is d. Since the convergent beam is emitted from the substrate side, it is incident and reflected from the other side of the paper surface.

Therefore, when viewed from the light source side, the land portion 3
Is concave, while the groove portion 4 is convex. When the groove surface is used as a phase reference, the phase of the reflected light from the land portion lags the reflected light from the groove portion by 2π · 2nd / λ. Here, n is the refractive index of the substrate, d is the depth of the groove, and λ is the wavelength of the convergent beam.

The phase change is not caused only by the groove depth, but generally the phase difference also changes by the change of the optical constants before and after the phase change of the recording layer. Here, it is assumed that the reflected light from the amorphous region is delayed in phase from the reflected light from the crystalline region by 2πα (α: phase difference). In the following, the amplitude reflectance of the convergent beam will be formulated using the phase difference α as necessary with the groove surface as the phase reference. As shown in FIG. 1, the amplitude reflectance φ ₁ when the convergent beam 5 is on the land portion 3 having no amorphous recording mark can be expressed by the following equation.

[0031]

[Formula 12] φ ₁ = R _c1 · exp [−2πi · 2nd / λ] + R _c2 · exp [−2πi · 0] (a)

Where R _c1 is the amount of reflected light from the land region 6 irradiated with the convergent beam, R _c2 is the amount of reflected light from the groove region 7 irradiated with the convergent beam, and n is the refractive index of the substrate. d is the depth of the groove, λ is the wavelength of the irradiation light, and i
Indicates an imaginary unit. As shown in FIG. 2, the amplitude reflectance φ ₂ when the convergent beam 5 is on the land portion having the amorphous recording mark can be expressed by the following equation.

[0033]

Φ ₂ = R _a1 · exp [−2πi (2nd / λ + α)] + R _c2 · exp [−2πi · 0] (b)

However, R _a1 represents the amount of reflected light from the region 6 of the land portion irradiated with the convergent beam, and R _c2 represents the amount of reflected light from the region 7 of the groove portion irradiated with the convergent beam. As shown in FIG. 3, the amplitude reflectance φ ₃ when the convergent beam 5 is on the land portion having no amorphous recording mark can be expressed by the following equation.

[0035]

[Mathematical formula-see original document] φ ₃ = R _c1 · exp [−2πi · 0] + R _c2 · exp [−2πi (2nd / λ)] (c)

However, R_c1Is the beam irradiated by the focused beam.
Amount of light reflected from area 7 of the lube, R _c2Is a focused beam
Shows the amount of reflected light from the illuminated land area 6.
You. Glue with amorphous recording marks as shown in Figure 4
Amplitude reflectance φ when there is a convergent beam 5_FourIs
Can be represented by

[0037]

Φ ₄ = R _a1 · exp [−2πiα] + R _c2 · exp [−2πi (2nd / λ)] (d)

However, R_a1Is the beam irradiated by the focused beam.
Amount of light reflected from area 7 of the lube, R _c2Is a focused beam
Shows the amount of reflected light from the illuminated land area 6.
You. Here, land width = groove width, which is the convergence width.
Since it is assumed that the diameter is half the diameter, 0 <β <1 is set.
When,

[0039]

## EQU16 ## R _c2 = βR _c1 (e)

[0040]

## EQU17 ## R _d2 = βR _a1 (f)

[Apply] R _c = R _C1 + R _c2 , R _a = R _a1
When formula (c) and formula (f) are rearranged as + R _a0 ,

[0042]

R _c1 = R _c / (1 + β) (g)

[0043]

R _c2 = βR _c / (1 + β) (h)

[0044]

R _a1 = R _a / (1 + β) (i)

[0045]

R _a2 = βR _a / (1 + β) (j)

It becomes Expression (g) to Expression (j) are replaced by Expression (a) to
Substituting into equation (d) and rearranging,

[0047]

Φ _i = [R _c / (1 + β)] [β + exp [-4πind / λ]] (k)

[0048]

Φ ₂ = [1 / (1 + β)] · [βR _c + _Ra · exp [-4πind / λ-2πiα]] (l)

[0049]

Φ ₃ = [R _c / (1 + β)] [1 + β · exp [−4πind / λ]] (m)

[0050]

Φ ₄ = [1 / (1 + β)] [R _a · exp (−2πiα] + βR _c · exp [−4πind / λ]] (n)

Here, when recording on the land portion, the reproduction carrier level CL '(L) is

[0052]

[Equation 26] CL '(L) = | φ ₁ | ² − | φ ₂ | ² (o)

Proportional to Also, when recorded in the groove section in the same manner, the reproduction carrier level is

[0054]

[Equation 27] CL '(G) = | φ ₃ | ² − | φ ₄ | ² (p)

Is proportional to The fact that there is no difference in the carrier level between the land portion and the groove portion means that the difference between the equation (o) and the equation (p) becomes zero. Substituting equations (k) to (n) into equations (m) and (o) to calculate the difference and finding the necessary condition for the difference to be 0, α = m
π (where m is an integer).

This result shows that when the phase difference between the phase transitions is an integral multiple of π (including 0), the reproduction signal amplitudes of the land portion and the groove portion are equal when the land width-the groove width. Shows. On the contrary, we intentionally made a disc with a layered structure with a phase difference between phase transitions,
We have been earnestly studying.

As a result, the inventors have found a new condition in which the signal amplitudes of the land portion and the groove portion do not differ even if the phase difference between phase transitions takes any arbitrary value. These conditions are those that limit the range in which the recording layer is the ratio of the specular portion reflectance R _a disk when the reflectance R _c and the amorphous state of the mirror surface of the disk when the crystalline state.

In the first place, when land width = groove width,
The difference in the reproduction signal amplitude between the land and the groove is related to the phase difference depending on the groove shape and the phase difference between the phase transitions, but the difference in the reflected light amount between the land and the groove (that is, the difference in the reproduction signal amplitude) is It is also highly dependent on the degree of interference effect depending on the ratio of reflectance between transitions. That is, assuming that one of R _C and R _a having a higher reflectance is R _high and the one having a lower reflectance is R _low , if R _low is sufficiently smaller than R _high , no matter how a phase difference occurs, it is practical. The difference in the amount of reflected light between the land and the groove due to interference is sufficiently small.

For the purpose of actually investigating this, we made a large number of discs having different phase differences between phase transitions and R _high and R _low , and examined their influence on the difference in the reproduced signal amplitude between the land and the groove. As a result, as shown in claim 1 of the present invention, in the disk with a limited range of R _high in the range of 10% to 40%, by R _high / R _low is 0.15 or less, the phase transition Even if the phase difference between values is arbitrary, L
It has been found that it is possible to equalize the signal quality of land recording and the signal quality of groove recording in & G recording.

The range of R _high / R _low necessary for this purpose can be specified by appropriately selecting the optical constant and the film thickness of each layer. Regarding the groove depth of the substrate, Jp
n. J. Appl. Phys. Vol32 (1993)
pp. As described in 5324-5328, the groove depth is λ / 7n to λ / 5n (λ: reproduction light wavelength,
Since n is the refractive index of the substrate, crosstalk from adjacent tracks is reduced, so that it is desirable to be in this range.

Here, a method of measuring the groove width and the groove depth will be described. Ne-Ne laser light (wavelength 630n is measured.
m) is radiated from the side of the substrate having no groove, and the 0th-order light intensity I ₀ , the 1st-order light intensity I ₁ , the 2nd-order light intensity I ₂ and the angle of the diffracted light obtained by diffracting the transmitted light by the groove of the substrate This is done by measuring. When P is the groove pitch, w is the groove width, d is the groove depth, λ is the laser wavelength, and θ is the angle between the 0th-order light and the 1st-order light, when the grooves are rectangular,

[0062]

[Equation 28] I ₂ / I ₁ = cos ² (πε)

[0063]

[Equation 29] I ₂ / I ₁ = { ² sin ² (πε) (1-cosδ)}
/ [Π ² {1-2ε (1-ε) (1-cosδ)}]

[0064]

[Equation 30] ε = w / P, δ = 2 (n−1) πd / λ
(N is the refractive index of the substrate)

[0065]

(31) P = λ / sin θ

Since the relationship of the above is established, the groove width and the groove depth are calculated. Although the actual groove shape is not a perfect rectangle, the groove shape in the present invention uses the values that uniquely determine the groove width and groove depth by the above-described measurement method. Therefore, the groove shape in the present invention is applied even when it is deviated from the rectangular shape. High signal quality is guaranteed regardless of whether the track is recorded on the land or groove.

A resin layer is preferably applied or spin-coated on the metal reflective layer according to the first aspect in order to protect the film. The dielectric used in the dielectric layer of the present invention can be variously combined, and the refractive index, thermal conductivity,
It is determined by paying attention to chemical stability, mechanical strength, adhesion, etc. Generally, Mg and C, which are highly transparent and have a high melting point,
a, Sr, Y, La, Ce, Ho, Er, Yb, Ti,
Zr, Hf, V, Nb, Ta, Zn, Al, Si, G
e, oxides such as Pb, sulfides, nitrides, Ca, Mg, L
Fluorides such as i can be used.

Of these, ZnS and SiO ₂ or Y ₂
When a mixed film of at least one of O ₃ is used, if the content of SiO ₂ or Y ₂ O ₃ is preferably 5 to 40 mol%, the storage stability of the recorded disk is excellent. The disk can be used as a single plate specification using only one surface, and the capacity can be doubled by bonding two disks with the surfaces opposite to the substrates facing each other.

In the case of a laminated disc, by adopting a drive having a structure in which optical pickups are set on both sides of the disc, both sides of the disc can be recorded / erased and reproduced at the same time without replacing the disc. This is an important feature that cannot be achieved with a magneto-optical disc that requires a magnet on the side opposite to the laser irradiation side. To design the disc of the present invention, it is necessary to accurately grasp the phase difference between the reflected light before and after the phase change.

Further, it is more desirable to accurately grasp the above-mentioned A _c / A _a and to set it within a certain range in terms of CN ratio and recording mark jitter. The phase difference can be measured with a laser interference microscope or the like. Since A _c / A _a is the absorptance ratio of only the recording layer in the multilayer structure, it cannot be known by direct measurement.

However, both the phase difference of the reflected light before and after the phase change and the absorptance ratio A _c / A _a can be calculated by using the optical constant and the film thickness of each layer. The calculation method is “Basics and Methods of Spectroscopy” (Kei Keiei, Ohmsha, 1985) 3.
It is described in detail in the chapter. The calculated values of the phase difference and the absorptance ratio in the present example and the comparative example were calculated based on the method described in this document.

The optical constants of the respective layers may be measured by an ellipsometer or the like after forming a monolayer film by a method such as sputtering in advance. Recording / erasing of the optical disc of the present invention
For reproduction, a one-beam laser focused by an objective lens is used, and irradiation is performed from the substrate side of the rotating optical disk. At the time of recording and erasing, a rotating disk is irradiated with a pulsed laser beam to change the recording layer into two reversible states, a crystalline state or an amorphous state, and a recording state or an erasing state (unrecorded state). To do.

At this time, by overwriting, it is possible to simultaneously erase the marks existing before recording while recording. At the time of reproduction, laser light having a power lower than the laser power at the time of recording and erasing is applied to the rotating disk. At this time, the phase state of the recording layer immediately before reproduction must not be changed. Reproduction is performed by detecting a change in the intensity of reflected light with a photodetector and determining a recorded or unrecorded state.

Now, after the good initial characteristics are obtained in the land and the groove as described above, it is desired to further improve the durability against repeated overwriting and the durability against the cross erase described above. . According to the study by the present inventors, the durability of the groove portion against repeated overwriting is better when the groove width is narrower, which is consistent with the higher track pitch. If the lower limit is set by force, the recording mark does not protrude from the inside of the groove, and the condition is defined in relation to the focused beam shape in, for example, Japanese Patent Laid-Open No. 6-338064.

However, it has not been mentioned that the durability against repeated overwrite is influenced by the groove width or the land width. According to the study by the present inventors, the repeated overwrite on the land is different from the land width. It was found that, depending on the relative relationship with the beam diameter, when the land width becomes significantly narrower than the beam diameter, it deteriorates rapidly.

Therefore, in the present invention, the land width is preferably 0.62 × (λ / NA) to 0.80 × (λ / NA).
Range. If the width of the land is narrower than this range,
When the recording mark is repeatedly overwritten on the land, the remaining mark of the previous mark becomes remarkable, and the jitter of the recording mark is significantly deteriorated.

When the land width is within this range,
There is no remaining unerased mark or marked deterioration of recorded mark jitter when repeatedly overwritten, and the same characteristics as when recorded in the groove are maintained. When the width of the land is larger than this range, there is no problem in the repeated overwrite characteristic of the land, and good characteristics can be obtained.
From the viewpoint of high-density recording, it is not a good idea to unnecessarily widen the land width to reduce the recording density.

Further, it was found that the cross erase phenomenon also depends on the relative relationship between the beam spot diameter and the recording track pitch. That is, there is a minimum track pitch that can reduce the cross erase to a practically negligible level, and it depends on the size of the beam spot diameter. Since the light beam spot diameter is proportional to λ / NA,
It can be considered that the minimum allowable pitch is proportional to λ / NA.

To be precise, the proportional coefficient may be determined experimentally. In fact, as a result of various investigations by the present inventors, the groove pitch of L & G recording was 1.2 (λ / N).
If it is larger than A), C / N after 10 ⁴ overwrites
The ratio (carrier-to-noise ratio) can be reduced to less than 3 dB, which is a level with no practical problems. Since the actual recording track pitch of L & G recording is half the groove pitch (groove pitch), the minimum recording track pitch is 0.6 (λ /
It has been experimentally confirmed that the signal deterioration of the adjacent track due to cross erase can be prevented if the ratio is larger than NA).

The above value of 0.6 is theoretically the value of the lens 9
This corresponds to exactly half of the beam spot of the convergent light 10 that has passed through. That is, the converged light beam 10 has a shape as shown in FIG. 5, and the intensity distribution (1 in FIG.
A sub-peak appears in the figure where 1 shows the intensity distribution). The diameter of the central spot is approximately 1.2 (λ / NA).

This is referred to as an airy disc.
sk) 12. The light intensity distribution in this is not uniform, and the diameter at which the intensity is 1 / e ² (e is the base of the natural logarithm) is expressed as 0.82 (λ / NA). Since the minimum pitch of the track 1 corresponds to the radius of the area disc, the cross erase phenomenon is the first approximation that the weak laser light at the foot of the Airy disc of the focused light beam spot as shown in FIG. The physical meaning that adjacent tracks are heated is also clarified.

The fact that the cross-erase phenomenon is hardly affected by the heat conduction of the recording layer is known to be GeS.
bTe, AgInSbTe, InSnTe, InSbT
e, etc., containing at least one of IIIb, IVb, Vb, VIb group elements or a mixture (alloy) thereof as a main component at 40 at. This is because the thermal conductivity of the recording layer containing 100% or more is on the order of two to three orders of magnitude lower than that of the magneto-optical medium. Then, it is substantially adiabatic on the order of 10 to 100 nanoseconds required for recording.

Therefore, the minimum track pitch determined by the above 0.6λ / NA is substantially the beam spot diameter, and
It depends only on the light beam wavelength and NA. However, although the cross-erasure after repeated overwriting 10,000 times is a little, further reduction can be achieved by limiting the layer structure of the recording medium and the physical properties of the recording layer.

Although it depends on the melting point and the crystallization temperature of the recording layer, the melting point Tm is 700 in the composition which is currently known to be capable of reversibly changing between crystalline / amorphous in the alloy recording layer. Many have a crystallization temperature Tg of 150 ° C. or higher and a crystallization temperature of less than 150 ° C. In fact, Ge ₁ Sb ₂ Te ₄ or G
In the vicinity of the e ₂ Sb ₂ T _s composition, the melting point is 600 to 620.
C., the crystallization temperature is 150 to 170.degree. Also, Ag
_0.11 In _0.11 Te _0.20 Sb _0.55 has a melting point of about 550.
C., crystallization temperature is about 230.degree. If the Tg is lower than 150 ° C., the stability of the amorphous state is poor and cross erase tends to occur.

If the Tm is 700 ° C. or higher, the energy to be applied during recording is high, and cross erase is likely to occur in the adjacent tracks. For the layer structure,
When the recording layer thickness exceeds 30 nm, the recording sensitivity decreases,
Moreover, since heat easily escapes to an adjacent track during recording, cross erase easily occurs. Examples are shown below,
The present invention is not limited to the following examples unless it exceeds the gist.

Example 1 A polycarbonate resin substrate was obtained as a substrate by injection molding. The substrate has a groove pitch of 1.3 μm
A plurality of sheets were prepared, each of which was changed up to 1.6 μm in steps of approximately 0.05 μm. Therefore, the actual recording track pitch is 0.65 to 0.8 μm. 2100Å of (ZnS) ₈₀ (SiO ₂ ) ₂₀ as a lower protective layer on the obtained substrate,
Ge ₂₂ Sb _23.5 Te _54.5 is 200 Å as the recording layer, and (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 200 Å as the upper protective layer,
As a reflection layer, Al _97.5 Ta _2.5 was formed by 1000 Å sputtering. An ultraviolet curable resin was further provided as a protective coat on the reflective layer.

Upon initialization, the state in which the entire surface is crystallized is set as an unrecorded state, and the recording mark is amorphous. The reflectance R _{high in the} unrecorded state is 14.2%, and the reflectance ratio R _low / R _high =
0.09, A _c / A _a = 0.91, phase difference of −0.44
π. The optical head has a wavelength of 680 nm and NA = 0.5.
5 were used. Linear velocity is 3m / s, Pw = 8 ~
It was set to 9 mW and Pe = 4.5 mW. The recording power is
Modulation was performed with a single pattern having a frequency of 2.24 MHz and a duty of 25%. When recording was performed on the groove, overwriting was repeatedly performed between the adjacent grooves to measure the decrease in the C / N ratio of the signal first recorded on the groove.

The same measurement was performed in the case where recording was performed on the land and the adjacent grooves were repeatedly overwritten. If the groove pitch is larger than 1.5 μm (recording track pitch 0.75 μm), the decrease in C / N ratio between adjacent grooves or between grooves after overwriting 10,000 times can be less than 3 dB, which is not a practical problem. It was a level.

(680 / 0.55) × 0.6 = 741n
m = 0.741 μm, which can be considered to be greater than the requirement 0.6 λ / NA for the minimum track pitch. on the other hand,
When a similar experiment was performed using a head having a 680 nm and NA = 0.6, there was no problem up to a groove pitch of 1.4 μm (recording track pitch of 0.7 μm). This is (680 /
The minimum recording track pitch condition of 0.6) × 0.6 = 0.680 μm is satisfied.

On the other hand, when recording was carried out on the land and the adjacent grooves were repeatedly overwritten and the deterioration of the signal on the land due to cross erase was measured, exactly the same result was obtained except for the difference of 1 to 2 dB. I got it. Further, the land was repeatedly overwritten, and the mark length jitter of the signal between the grooves was measured. In this case, λ = 680n
The measurement was performed only with a head having m and NA = 0.55. Only when the groove pitch was 1.6 μm (land width ≈0.8 μm), there was almost no increase in jitter after 10 ³ overwrites (only about 20% increase). In this case, the land width is wider than 0.62λ / NA≈0.77 μm, which satisfies the requirement of the present invention. On the other hand, groove pitch 1.4μ
At m (land width 0.7 μm), the jitter was remarkably increased, and it was more than doubled after 10 ³ overwrites.

According to the analysis result obtained by solving the thermal diffusion equation of the present inventors by numerical calculation, the layer structure used in this example has one of the largest thermal diffusions in the lateral direction. It means that we are considering the strictest conditions regarding erase. Therefore, it can be considered that the above-mentioned regulation on the minimum track pitch is established regardless of the layer structure.

[0092]

As described above in detail, according to the optical recording medium and the recording / reproducing method of the present invention, even if a signal is recorded on both the land and the groove, the groove depth is limited, so that the adjacent tracks are adjacent. Crosstalk from can be reduced. Further, since the ratio of the reflectance of the reflected light from the unrecorded area to the coherent light having the same wavelength as the reproduction light and the reflectance of the reflected light from the recording area is defined, the recording mark of the land portion The undesired difference between the carrier level and the carrier level of the groove part can be eliminated.

Therefore, a reproduction signal amplitude of the same level can be obtained regardless of whether recording is made on the land portion or the groove portion, and a high quality and highly reliable land groove recording disk can be provided. Further, the ratio of the irradiation light absorbed by the recording layer when the recording layer of the optical recording medium of the present invention is in the amorphous state, and the irradiation light absorbed by the recording layer when the recording layer is in the crystalline state. When the recording layer is in the amorphous phase and A _a is in the case where the recording layer is in the amorphous phase, and A _c is in the case where the recording layer is in the crystalline state, the ratio of absorption A _C / A _a between the crystalline state and the amorphous state is

[0094]

(32) 0.84 ≦ A _C / A _a <1.01

By defining the ratio in the range of, it is possible to guarantee excellent characteristics with a high CN ratio and low recording mark jitter, and it is possible to provide an excellent disk. Furthermore, by using the optical recording medium of the present invention, both on and between the grooves are used as recording areas, and recording and erasing in both areas by one beam overwriting of a laser having a wavelength of 700 nm or less,
It is possible to provide a recording / reproducing method characterized by reproducing.

[Brief description of drawings]

FIG. 1 is an enlarged perspective view for explaining a groove shape of an optical disc and a positional relationship of a converged beam of an irradiation laser beam in an example.

FIG. 2 is an enlarged perspective view for explaining the positional relationship between the groove shape of the optical disc and the convergent beam of irradiation laser light in the example.

FIG. 3 is an enlarged perspective view for explaining the positional relationship between the groove shape of the optical disc and the convergent beam of the irradiation laser light in the example.

FIG. 4 is an enlarged perspective view for explaining the positional relationship between the groove shape of the optical disc and the convergent beam of the irradiation laser light in the example.

FIG. 5 is an explanatory diagram of intensity distribution of a converged light beam.

[Explanation of symbols]

 1 Substrate 2 Recording Layer 3 Land Part 4 Groove Part 5 Convergent Beam 6 Convergence Beam Area Irradiated to Land 7 Convergence Beam Area Irradiated to Groove 8 Recording Mark 9 Lens 10 Convergent Light 11 Intensity Distribution 12 Airy Disc

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tohwa Horie 1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa Mitsubishi Chemical Corporation Yokohama Research Institute

Claims (6)

[Claims] 1. A transparent substrate on which a groove is formed, and a dielectric layer, a phase-change recording layer, a dielectric layer, and a metal reflection layer are sequentially laminated on the transparent substrate, and the recording area is formed on both the groove and the land. An optical recording medium for recording, erasing and reproducing information by irradiating a laser beam having a wavelength of 700 nm or less, wherein (1) the groove width is 0.3 μm or more and 0.8 μm or less and the land width is 0 .3 μm or more and 0.8 μm or less and the groove depth d satisfies the following inequality: λ / 7n <d <λ / 5n (λ: wavelength of irradiation light, n: refractive index of substrate, d: depth of groove) (2) Of the reflected light from the unrecorded area and the reflected light from the recorded area defined below, the one with the larger reflectance is R.
_{If high} (%) and the lower one are R _low (%), and the phase difference between the reflected light from the unrecorded area and the recorded area is α, the following expression is satisfied: ## EQU2 ## 10 ≦ R _high ≦ 40 R _low / R _high ≦ 0.15 mπ ≠ α (m is an integer) where α = (phase of reflected light from unrecorded area) − (phase of reflected light from recording area) (3) The land width LW satisfies the following expression: 0.62λ / NA < LW < 0.8λ / NA λ is the irradiation light wavelength, NA is the numerical aperture of the focusing lens (4) The groove width GW and the land width LW are An optical recording medium satisfying the following expression: (LW + GW) / 2> 0.6λ / NA. 2. The ratio of the absorbed laser light of wavelength λ absorbed by the recording layer is A _d when the recording layer is in the amorphous phase and A _c when the recording layer is in the crystalline state, Absorption ratio of crystalline state and amorphous state A _c /
The optical recording medium according to claim 1, wherein A _a is 0.84 ≦ A _c / A _a <1.01. 3. The recording layer is made of an alloy containing Ge, Sb, and Te as a main component and has a thickness of 20 ± 5 nm.
Or the optical recording medium according to 2. 4. The reflection layer is an alloy of Al and Ti or Ta, and the content of Ti or Ta is 0.5 to 3.5 at%.
The optical recording medium according to any one of claims 1 to 3, wherein 5. One or both of the lower dielectric protective layer and the upper dielectric protective layer comprises ZnS and SiO ₂ or Y.
SiO 2 is a mixed film with one of ₂ O ₃ and
The optical recording medium according to claim 1, wherein the content of ₂ or Y ₂ O ₃ is 5 to 40 mol%. 6. The optical recording medium according to claim 1, wherein both the groove and the groove are used as a recording region, and recording and erasing are performed in both regions by one-beam overwriting with a laser having a wavelength of 700 nm or less, A recording / reproducing method characterized by reproducing.